Relays enabled with multiuser MIMO techniques have great potential to mining vehicle safety applications. However, they are yet to be practical due to high scheduling overhead in mobile, radio-unfriendly, mining environments. A new decentralized relay-assisted multiuser MIMO approach is proposed, which cuts the overhead by 80% and enables relay-assisted multiuser MIMO to be implemented in practice. This approach is a new distributed participatory downlink transmission method, where both the relays and destinations participate in the scheduling decisions. A new recursive algorithm is also developed to optimally quantize the channel conditions of the vehicles, thereby minimizing the feedback requirement. Analytical results, confirmed by simulations, show that the proposed approach is able to achieve 97.6% of the sum-rate upper bound of the network, using only three bits to characterize the channel condition of each vehicle. In terms of throughput, the proposed decentralized scheme can perform 45.2% better than the existing centralized scheme. The proposed approach is compatible with industrial communication standards and can be implemented with commercial industrial communication systems.